Process of sherardizing.



E. F. COLLINS & J. A. CAPP.

PROCESS OF SHERARDIZING.

APPLICATION FILED MAR-17,1914.

5 169 528, Patented Jan. 25, 1916.

In ventors John A.Cap p -Edgar F. CoHms,

Their fittorneg.

. cry small percentage of dent that a very to the charge so that the "be heated throughout powder, which is an artificially produced atomized metallic zinc, containing only a zinc oxid or impurities. When this, zinc powder is first used in th sherardizing drums a blank run is first made, that is to say, without any articles being packed in the drums for sherardizing, whereby the oxygen 'presentkin the air in the drum combines with zinc to produce zinc oxid. Upon conclusion of' thisheat treatment, the zinc dust is submitted to chemical analysis and it its lic zinc is found to fall within the. limits of 89% to 92"", it is then ready for use. k hould the zinc content be too low then the proper proportion of metallic zinc in the orm of, powder is added audit the zinc content is too high then the charge is reheated to produce further oxidation. As the content of metallic zinc in the charge is reduced by repetitions of the sherardizing, operation, it is necessary to make up for this by regularly addin I runs in quantity sulii cient to keep themetallic zinc content Within the limits indicated. This quantity is determined after careful chemical analysis of the charge which analyses shouldl7e made at frequent intervals.

The temperature which we employfor sherardizing with. the zinc dust mixture of the richness'indicated, we find should lie- Within relatively small limits, the lower limit of temperature being 350 and the the upper limit 375911., though a very slight variation either way may be tolerated. With Such a close temperature range within which to carry on the sherardizing, it isvriv special type of furnace is necessary so that the temperature may he raised uniformlythroughout the charge to the operating temperature and maintained very closely the same throughout the entire char 0. Any material variations oii' i-he opcrating temperature from the range t temperature which'we have indicated "Ill-Tesult in an inferior son it has been found to lie-practically impossible tocarry out our process with ordi-' nary typesof gas or oil heated furnaces heretofore used for sherari Egg The funace which we lrztliftuud best adapted to the carrying out at ain: process is a furnace making use of electrically produced heat. The heating coils or conductors may helocatcd at proper points in relation entire charge may very closely to the sametcmperaturea In the drawings we have illustrated, lay way of example, afurnace suitable for use in carrying out our improved' process.

In general the furnace consists of a hex of suitable construction for containing thev charge; mounted on trunuious so'that it may be rotated, and provided with electric l10atcontent of metaL zinc powder between product, and for this reaand is provided with a cast'ircn cover simi- "larly indicated at Upon each of the five sides of the box, and upon the cover, heating units made of strips of sheet metal or other suitable material are applied as indicated for example at 3. These heating units are held in place by metal clamping plates such as 1'', and are insulated both from the box and the clamping plates by sheets of insulating 1X19," terial such as 5, 6 consisting" of huiltaip sheets of micav or the like. on the cover of the box lated from the cover clamping plate 7. box proper, as well as its cover, is provided with an outer shell or casin g of sheet metal. The casing for the box proper is indicated at 8 and for the cover the casing is indicated at 9. These are so applied as to provide a considerahiespaee hctween the'casing" and the members which they inclose, and in this'spaee heat insulating material such as asbestos, mineral wool or the like is placed asindicated, for example'at 10 and 1].

The cover of the furnace box is held in place by any suitahleineans, such for example ass-clamping bars 12: and -13, the ends of which project through slots in lu s- 14- formcd integral with the hex l. and project ing up through appropriate openings inthe cover. Clampingscrews indicated at Nil screw down upon homes or lugs 17 which are formed integral with the cover plate 2 and project up through openings in the sheet iron casing 9. Ring'holtsltl are provided whereby the cover may he lifted when the clamping dcviceshave been removed.

,The entire here is mounted upontrunniony gg'g onev at whim is indicated at 19, these aunt; nions being carried-by pillow hloclrsor otir hearings 28. Some suitable gearing isfp vidcd, such for example as a worm and Warm wheel 21 and 2'2, for setting-the loo into slow rotation. Coliector rings are similarly insuwhereby the heating units may he connected in series or in multiple, in order to provide T he heatin units 2 and the cinrespondii'igvv inc 24;, and 25. mounted on a progectrnp; shaft 26, and proor operating temperature coating will bear to for current adjustment. Thus, upon starting up she apparatus, the heatiugunits may be connects/din two sections in multiple with each other, and when the desired temperature is reached the connections may be changed to series, further adjustment being taken care of by appropriate external regulators.

In order that the temperature of the charge may be properly coniarolled, thermometers are placed injiubes such as 27 extending through the we lscf rhe-iurnace box into close proximity he she charge. A well known form of angleeherrnometcr is indicated at 28. I

It is imporiant, in carrying out our'process, that the temperature of the charge in the sherardizing drum or furnace should be raised as quicldy as possible to the working for the reason that the sberardized coating which is deposited at temperatures iower than this working temperature is inferior, and hence the shorter she time taken in reaching the working temperature the ism proportion this inferior the total. For this pur sherardizing operation, the electric current applied to the heating coils l'inade very much greater at first than after'ighc desired temperature of the charge has been reched. ture has been reached, the heating current is cut down until only just enough energy is supplied to make up for the heat losses. When the desired working temperature of 350 C. to 375 C.-has been attained the electric current is controlled so that the temperature of the charge will remain within the limits noted. The temperature of the charge is preferably ascertained by means of shermometers inserted into the charge through openings in the sherardizing box or drum as already described. The readings of these thermometers will obviously vary somewhat but all ought to lie within the range above noted.

The length of time for carrying out the sherardizing operation accordingto our process varies somewhai according to the thickness of coating desired but runs anywhere from (i to 12 hours.

If during the sherardizing operation the temperature s allowed to rise materially above 375 (1. we find that the deposit or coating becomes coarse and crystalline, whereas if the tempo atureis allowed to fall materially below the lower limit of 350 0., the coating becomes relatively soft and porous. in both cases the coating is decidedly inferior. lvloreover, good results will not be secured even within, the rernpeuture range we have indicated unless .ie composition of the mixture is such that the mecallic zinc pose, in starring the content iswirhin the range of 80 to 92%.

If there is more metallic Zinc present than that represented by the upper limit of ap- When this desired temperaproximately 92%, the mass of powder becomes sticky and pasty so that the proper coating does not take place, while if the mixture has a less percentage vof zinc than about 80% thenthe sherardized coating is of less definitely metallic character being therefore like the soft and spongy coat applied at too 105v temperature, and incapable of withstanding corrosive action.

The sherardized coating produced according to our process wherein the composition of the Zinc dust and the temperature of shelf ardizing are correlated as above described, is never lumpy or uneven in thickness as frequently ha ipens when the. temperature and composition of the zinc mixture are not controlled as w have set forth. On the contrary the coating is so smooth, even and uniform in thicknkgss, that. by proper time allowance a coating of any desired thickness may be applied with great exactness. This makes it possible to sherardize articles like" nuts and boips so that the threads fit'exactlyj without, as has quiring the smoothing action of taps or dies to smooth off the threads, a proper under cutting of the threads having been made to compensate for the subsequent application of the coating. Also, our improved sherardized coating'is far superior in resisting corrosion to the sherardized coatings heretofore produced. One distinguishing char acteristic of shera'rdized coatings made in accordance with-our process is that of color. For example, malleable ironcastings, when they have been submitted to treatment according to. our process,'have a color almost black, or which might perhaps be described as a very dark 'aud dingy gray. The color is entirely distinct from that cliurapt cristic or" the ordinary sherardizing which is a light, and in some cases is a veryiight, silver gray. In the case of a malleable iron or similar casting treated by our process. the article after removal from the sherardizing drum or furnace does not appear greatly difi'crent in color from that which it possessed before treatment. In fact, to the unpractised eye,

our improved sherardizing does notappear Y tp have changed the color of the article in a very marked degree. Upon careful cleaning of the sherardized article, however, moving any adherent particles of dust by rubbing, the sherardized coating appears to be not so much black as bluish, which is the characteristic color of pure zinc metal. The dark color of the sherardized metal produced by our process is perhaps cxplainable by the fact that it contains such a large percentage of pure nine and so little zinc cxid. This is indicated by the specific gravity of the coating which, in the case of that plied according-to our method, is exceed ingly high and in the neighborhood of 6.5 to

6.75 as compared with the specific gravity of pure zinc which is7.15. Sherardized coat- ,with sherardized coatingsas heretofore apings of lighter color such as heretofore proplied, but remains an. integral part of the duced, have a specific gravity much lower article. r

and averaging perhaps in the neighborhood What we claim as new-and desire to se- 5c 5 of 3.5. cure by Letters Patent of the United States, 7 Our improved sherardizing coating is far is za superior to the ordinary coating in its ca- I l. The method of sherardizing which conpacity to resist .corroding influences. An sists in submitting the articles to be sher-' ordinary test for measuring the value of ardized to the action of zinc dust or powder 10 zinc coatings in this respect, known .asthe containing not less than 80% nor more than Pree'ce test, consists in dipping the article in metallic zinc, the remainder being a solution of copper sulfate, washing and mainly zinc oxid while maintained. at a drying, and then repe'ating, the operation, working temperature which does not fall be until the coating breaks down. With this low 350 0. nor rise above 3755 C. so test applied, coatings made by our im- 2. The method of sherardizing which conproved process are able to withstand eight sists in so correlating the composition of the to twelve dips Whereas the prior sherardized .zinc dust or powder-and the working temcoatings were able to withstand. only one to perature of treatment that the percentage five dips under the same conditions. We of zinc in the dust lies withinthe limits of c have found, however, that the Preece test is about 80% to 92%, while the temperature of notinall respects a true indication of the treatment lies within the range between capacity of the coating to resist ordinary about 350 C. and 375 C. (-m roding influences such as sea water, sea The improvement in the art of shcrardair, etc, and we have devised a test wherein izing which consists in maintaining the shew 7o the length of time during which the article ardizing temperature so that it does not exis capable of resisting certain corroding in ceed 375 (1. or fall below 356 while "the tluences is more nearly a true measure of the zinc dust is maintained substantially 1 cc "lastin qualities of the coating in ordinary from impurities and with a percentage of use. %Ve provide a box or closed space in metallic zinc within the limits of 89% 75 which by means of an atomizer operated by compressed air a light spray is produced 41A metallic article having a'sherardized from a strong brine, or salt solution The zinc coating capable of resisting rusting inarticles to be tested. are placed on a grating fiuences indefinitely, said coating having a in this salt spray. Under this treatment, we specific gravity of not than (2.5, a color so have found that ordinary sherardizing lasts approximating that of an ordinary malleonly a few hours, at most only two or three able iron casting and a union with the metaldays,. whereas our improved sherardizing lic article such that the coating does not will last indefinitely, without breaking down, crack, flake or peel oil. when the. article and showing rust. deformed by bending, swaging or the like, 8 l0 The mechanical properties of shcrardized In witness whereof, we have hereunto coatings made by our process are also noteour hands this 16th day-of March, 1-914.

worthy. Articles so coated may be bent, EDGAR F. COLLINS. swaged or otherwise deformed, at ordinary JOHN A. L /APP, room temperatures, without injury to the Witnesses:

5 coating. The coating does not crack or BENJAMIN B. HULL,

flake oil, as has been found to be the "case HELEN Onronn. 

